from one amp. May sound a silly question, maybe something I should know but I have a Denon AVCA1SE and want to know how to run 2 subs from it and if it would benefit my room (dedicated 15x11) concrete floor
Running two subs from the amp is simply a case of getting a Y splitter for the line level sub out on the amp, its no big deal at all. You can get them from maplin and probably most good Hi Fi shops. Whether running two subs will benefit you is another matter.
The logic is that if you are going to get a two sub set up you should make them identical subs- buy the same sub you have now again- But before doing this you should probably consider if you are happy with the performance of your current sub. If so, buying another sub should give you a more enveloping bass experience. It will reduce the number of hot & cold bass zones in your room- IE in my room sitting to one side increases the amount of bass heard. Clearly adding a second sub will also allow you to have a lot more bass overall- Explosions and impacts can be louder before your sub starts to show the strain; All bass should sound a bit cleaner due to the reduced efforts of each individual sub- BUT having a second sub will not eliminate the weaknesses of the first. If your sub isn't doing anything for you now down at 20hz, it won't be helped by a twin brother.
There has been some debate on a similar subject by people more knowledgeable than me on this thread.
In my opinion, if you are thinking about buying two new subs in order to do this then you are probably better off buying one of Uncle Eric's Servo-Controlled Velodyne Godzilla family. Hell, get two. If you already have a good sub, then its a tough call.